Hi Richard,

I don't think it was particularly unusual to have a child or children out of wedlock. In the IOM there were many recorded, but a lot of their parents married after the birth. It was the custom in the IOM to use the father's surname, even if the parents didn't marry later.

I think you wrote in a message that you have the birth cert for Richard Thomas Corlett b.1926? That might give a clue, although I have seen births which later clearly were illegitimate, yet both parents were given in the official cert (sometimes correctly, but occasionally couldn't be found - invented?). In England they didn't seem to do any marriage checks like they did in some other places when the birth was registered.
I have an English birth cert where the child went to live with her grandparents in the IOM, and her birth cert had a different forename for her father than the one she gave for him when she married, and different occupations.

I had a look for your family in the 1911 census, Findmypast:
Name Relation Condition /Yrs married Se x Age Birth Year Occupation Where born
CORLETT, Thomas R Head Married M 53 1858 Mason Foxdale IoM
CORLETT, Margret Elizabeth Wife Married 24 years F 53 1858 House Wife Santon IoM [4 children born alive, 4 still living]
CORLETT, John Son Single M 17 1894 Masons Apprentice Castletown IoM
CORLETT, Stephen Sandford Son M 12 1899 Saddlers Errand Boy School Castletown IoM
MANTOVA, Stephen Nephew Single M 15 1896 Masons Apprentice Douglas IoM
RG number: RG14
Piece: 34650
Reference: RG14PN34650 RD635 SD3 ED19/1 SN147
Registration District: Isle of Man
Enumeration District: 19/1
Parish: Malew
Address: 126 Malew Street Castletown Iom [had 6 rooms, not counting bathroom, landing, etc.]
County: Isle of Man

BL's births index has these two MANTOVA entries:
John Stephen MANTOVA, b.9 Oct 1895, [regt]Douglas, [father] John William MANTOVA, [mother] Annie QUINNEY
William Percival MANTOVA, b.1 Sep 1898, Dou, John William MANTOVA, Annie QUINNEY

IGI has:
name: John William Mantova
event: Marriage
event date: 14 Jul 1894
event place: Braddan, Isle of Man
gender: Male
marital status: Single
father: Stephen Mantova
spouse: Annie Quinney
spouse's marital status: Single
spouse's father: John Quinney
digital folder number: 004494827

Still trying to work out how he could have been Thomas CORLETT's nephew, other than through his wife.

Sue